Methods and optical arrangements with which the intensity of a light beam is adjusted are known in practice. A widespread option in this case involves the use of acousto-optical tunable filters—or AOTFs—which vary the intensity of an excitation light in laser scanning microscopes, for example.
In this process, acoustic sound waves—usually in the radiofrequency range—are applied to an optical crystal via a transducer, wherein the sound waves cause periodic modulation of the local refractive index of the crystal. This modulation acts like an optical grating or Bragg grating and is able to diffract light with a corresponding wavelength. The speed with which such an acoustic wave can be modulated, together with the low costs of acousto-optical tunable filters in comparison with other methods, such as methods based on electro-optical effects, mean that they have become the standard tool for light modulation in laser scanning microscopes, for example. Acousto-optical tunable filters for laser wavelengths in the visible range are very widely used, but there are also embodiments for infrared—multiphoton microscopy—or ultraviolet light.